Gearless rotary mill



Sept. 13', 1966 E. A. E. RICH ETAL GEARLESS ROTARY MILL Filed Aug. 28,1963 5 Sheets-Sheet 1 mug 1E mllmullik in v6)? 6 0215'. Edward/1.5 R/c zc/ohn dfirackman,

4! 4 m The/'2" Attorney,

Sept. 13, 1966 Filed Aug. 28, 1963 IHIIIIIII IIIIIIIII" m 1 m I -n v v r1 I i i 1 E. A- E. RICH ETAL GEARLESS ROTARY MILL 5 Sheets-Sheet 2 [nyer/250215.: Zc/ward/ZZT fi/c/v, John cffirockman,

7772/)" At torney.

United States Patent N.Y., assignors to General Electric Company, acorporation of New York Filed Aug. 28, 1963, Ser. No. 305,076 6 Claims.'(Cl. 241-176) Our invention relates to a direct driven rotary millapparatus of the low speed, high torque type, and in particular, to themeans for mechanically coupling the mill to the rotor of the drivingmotor and the means for providing a suitable electric power supply tothe motor.

Rotary mills are a type of apparatus especially useful in applicationsWhere it is necessary that movement or agitation be imparted to thecontents of a rotatable receptacle. The receptacle may have any ofvarious forms depending upon the particular application. Suchreceptacles are often relatively large and comprise heavy metallicmembers having a weight of many tons. Rotary mills such as ball millsand rod mills find application in the grinding departments of cementindustry and ore concentrating plants. Other applications of rotarymills are the cooling, heating, mixing, or chemically combining ofcontents within the receptacle.

The unbalanced movement of the material being ground within ball millsnecessitates a low mill speed. The mill speed varies inversely with millsize (weight) and is typically in a range of 10 to 40 revolutions perminute (r.p.m.). The largest mills, as presently existing, weigh severalhundred tons, and have maximum mill speeds of approximately 1020 r.p.m.Such large mills require driving or mill motors having ratings ofapproximately 4500 horsepower. The conventional mill motors are of thesynchronous type and are electrically energized from essentially fixedfrequency alternating current power systems. Such energizing means arenot economically suited to provide the large amounts of controllable lowfrequency power required for gearless drives. Thus, the armatures ofconventional synchronous and squirrel cage induction rotary mill drivemotors are energized with 60 cycle power and such mill motors in generalhave a speed rating in the range of 150-1200 r.p.m. The significantdifference in speeds of the mill motor and mill requires a geararrangement therebetween to obtain the necessary low mill speed. Thegearing with its line-up problems-both initial and during operationandattendant lubrication systems develop substantial maintenance problems.Further, a higher kilovolt-ampere consumption is required to start,accelerate, and pull into synchronous speed the conventional gear drivenball mill. Finally, the space requirements for the gear assembly extendsthe over-all length of the mill and driving arrangement. Thus, theelimination of the gears would provide many advantages over the rotarymills now in use and would also permit the maximum size of the mill tobe increased greatly beyond present built limits of about 4500horsepower.

Therefore, an object of our invention is to provide a gearless typerotary mill wherein suitable frequency conversion equipment permits lowfrequency energization of a low speed mill motor.

Although gearless rotary mills are known, their use has been verylimited, and is unknown up to the present time in large size mills ofthe type employed in the cement industry, for example. In known gearlesstype rotary mills, the rotatable receptacle forms part of the rotor ofthe driving motor.

The disadvantage of such gearless rotary mill becomes apparent duringthe initial period of operation of the mill at which time unequaltemperatures and rates of temperature rise occur in the receptacle androtor windings attached thereto.

The

3,272,444 Patented Sept. 13, 1966 differing temperatures may induce highmechanical stresses within the motor rotor and also vary the air gapbetween rotor and stator poles. The stresses may be so severe as toshear some of the retaining bolts of the rotor. Further the induced highstresses in the rotor tend to produce an air gap at the rotor split inthe case of split rotor motors. Such split rotor and statorconfigurations are generally employed in large size motors for ease intransportation and handling.

Therefore, another object of our invention is to provide a gearless typerotary mill apparatus wherein changes in the rotor-stator air gap andmechanical stresses within the motor rotor resulting from unequaltemperature variation during mill operation are minimized.

Briefly stated, our invention provides a gearless type of rotary millwherein the rotor of a low speed electric motor is spaced from arotatable receptacle and is mechanically coupled thereto. In a firstembodiment of our invention, the motor encircles the receptacle and therotor is mechanically coupled to and supported from the receptacle bymeans of a plurality of resilient members. Such resilient membersminimize mechanical stresses which would otherwise be developed withinthe rotor and rotor supporting members by nonuniform expansions andcontractions produced as a result of unequal rates of temperature changewithin the respective structures and the receptacle. The rotorsupporting members may be nonresilient in cases where the dilferentialpressures and their effects are not large or Where the temperaturechanges encountered are relatively small. A second embodiment of ourinvention comprises an arrangement of the rotary mill and motor whereinthe motor does not envelop the mill but is aligned therewith and axiallyspaced therefrom.

The low speed synchronous motor which drives the rotary mill isenergized by means of static type frequency converter power supply whichconverts power generally available at a frequency of 60 cycles to asubstantially lower frequency.

The features of our invention which we desire to protect herein arepointed out with particularity in the appended claims. The inventionitself, however, both as to its organization and method of operation,together with further objects and advantages thereof, may best beunderstood by reference to the following description taken in connectionwith the accompanying drawings wherein like parts in each of the severalfigures are identified by the same reference character and wherein:

FIGURE 1 is a perspective view, partly in section, illustrating a firstembodiment of our invention wherein the rotor of a driving motor isspaced from and mechanical-1y coupled to an end portion of a rotatablereceptacle;

FIGURE 2 is a perspective view, partly in section, of a secondembodiment wherein the rotor is spaced from and coupled to anintermediate portion of the receptacle by means of resilient members;

FIGURE 3 is a detail side view of the resilient members shown in FIGURE2;

FIGURE 4 is a third embodiment of a gearless rotary mill wherein thedriving motor is axially spaced from the receptacle and is supported bya mill trunnion bearing; and

FIGURE 5 is a fourth embodiment wherein the driving motor is axiallyspaced from the receptacle and is supported entirely by its ownbearings; and

FIGURE 6 is a one-line electrical diagram of the frequency converterpower supply and motor circuit energized thereby.

Since our invention resides in the broad idea of employing an electricmotor as a driving unit for the rotation of a rotary mill without theuse of intervening transmission gearing, and since the selection of theprop- 'from mill shell 2.

er type of motor is a matter of engineering design to one skilled in theart, we have not illustrated the same in detail. Furthermore, althoughour invention is useful' in various types of rotary mills such as rodmills, tube mills, apparatus for roasting, cooling, or burning cement,and mixing cement, we have illustrated the rotary mill as a cylindricalball mill in as simplified detail as possible.

In FIGURES 1, 2, 4, there is shown a ball mill designated as a whole bynumeral 1, and comprising a rotatable receptacle or mill shell 2 ofcylindrical shape although other forms such as conical ended andhemispherical ended may be employed. Ball mill flanges '3 of theexternal type shown in FIGURES 1, 2, and 5 or the internal type shown inFIGURE 4 form the end portions of the ball mill. The ball mill issupported on either end by mill heads 4 which are aligned therewith. Thelarge diameter end of each mill head is provided with a mill head flange5 which is bolted to ball-mill flange 3. The small diameter end of eachmill head is connected to a hollow mill trunnion shaft 6 which isrotatably supported by mill trunnion bearing 7. The material to beground is introduced into the ball mill by being fed into hollow shaft 6at one end thereof and is discharged therefrom by passing through thehollow shaft at the opposite end thereof, one example being indicated bythe arrows in FIGURE 1. For the example illustrated in FIGURE 5, thehollow shafting for conveying of material in process can also terminateon the mill side of coupling 22.

Referring in particular to FIGURE 1, a low speed electric motor 8 of thealternating current synchronous type is shown disposed in concentricrelationship with an end portion of ball mill 1. Motor 8 comprises astator 9 and a rotor 10. Stator 9 is a conventional motor armaturewinding, and rotor 10 a conventional motor field winding, although itshould be understood that such windings may readily be interchanged.Stator 9 is stationarily mounted on a foundation 1 1 which also supportsthe trunnion bearings 7. The disposition of rotor 10 relative to millshell 2, and the means for mechanically coupling such members comprise asignificant part of our invention. In the first embodiment of ourinvention as illustrated in FIG- URE 1, rotor 10 is spaced from millshell 2 and attached to an end portion of mill 1 by means of an offsetrotor spider 12. Although spider 1-2 is shown as being connected to millflange 3, it may alternatively be connected to head flange 5. Rotorspider 12 comprises a hollow cylindrical offset web member 13 which isconcentric with mill 1, and radially extending members 14, 15 which arewelded to web 13 at each end thereof. Member 15 extends radially outwardof web 13 and is connected to the rim of rotor 10 in a suitable mannersuch as by welding. Member 14 may be of solid disk form or split. It mayalso have openings therethrough as required. Member 14 extends radiallyinward of web '13 and is attached to mill flange 3 by means of a rabbetfit and nut-bolt arrangement wherein the bolts pass through mill flange3 and head flange 5. In like manner, web 13 may be offset in theopposite direction from that illustrated, that is, away Finally, theremay be no offset at all, that is, a single radially extending web membermay be employed as a rotor support member. This latter form has theleast resiliency of the'various arrangements described herein, and wouldbe classed as essentially a nonresilient rotor spider.

mechanical stress in the rotor support members and rotor structure dueto differential expansion or contraction of the various parts. Suchchanges in dimensions are occa- SlOI16d by differential temperaturesbetween motor rotor and mill mounting parts arising from the unequalrates of temperature change sustained by such various parts. Inparticular, the temperature rise in the motor invariably occurs at adifferent ratio and stabilizes at a different operating temperature thanin the mill. The unequal rates of temperature change are especiallypronounced during the period of initial mill operation in a cold ambientatmosphere. In the absence of means for compensating for such thermalexpansions and contractions, the driving motor may have poor operatingcharacteristics, and in the extreme case, may be physically damaged. Inparticular, in the case of a split rotor-split stator motor, the boltswhich join the two rotor halves can undergo a severe stress and resultin an air gap formation at such rotor split. The air gap between therotor and stator may also be adversely affected by such differentialexpansions and contractions. Spider 12 may provide a rigid support forthe motor rotor or may be designed to compensate for differentialexpansion and contraction of the mill and motor rotor with varyingtemperature. A rigid rotor support is obtained by manufacturing radiallyextending member 15 in the form of a solid or split disk, or a disk withopenings therethrough for handling and other purposes. A resilientoffset rotor support which is adapted to compensate for thermalexpansion and con-traction,is provided by manufacturing member 13 in theform of a comparatively thin cylinder, with or Without openings in itbut welded to members 14 and 15. Another form of a resilient offsetrotor spider construction includes member 15 in the form of spokesarranged somewhat tangentially as illustrated in FIGURE '3, or of thecombination of a thin cylinder for member 13 and the spokes for member15. As another example, member 15 may be a solid disk, and members 13,14, 15 are manufactured from sufficiently thin steel to provide thedesired resiliency.

A specific example of the apparatus illustrated in FIG- URE 1 consistsof components having the following approximate dimensions: ball mill 1has a length of 3 6 feet, diameter of 17 feet and weighs 300 tons. Motor8 is a 6000 horsepower, 12.8 rpm, 1080 volt, 3 phase, 7.7 cycles persecond synchronous motor having a rotor inner diameter of 22 feet, astator outer diameter of 30 feet and an axial length of six to sevenfeet. Member 15 consists of a three inch thick radial disk. Disk member14 has an inner diameter of 17 /2 feet, outer diameter of 19 /2 feet,thickness of five inches and is constructed of low carbon or mild steel.For the resilient case, spider web member 13 is manufactured of two inchand is 45 inches in axial length. A relatively rigid connection betweenthe rotor and mill is utilized in applications where differentialpressures and their effects (forces), produced by unequal temperaturesare of relatively small magnitudes, such as obtained from temperaturedifferences as large as approximately 30 F. A rigid coupling of therotor to the mill in the above example is obtained by constructingmember 13 in the form of a four inch thick cylinder.

FIGURE 2 illustrates a second embodiment of our invention wherein thedriving motor 8 encircles the mill shell 2 in a region intermediate theends of the ball mill. Rotor 10 is illustrated as being of the splittype, it being understood that the rotor and stator of all theillustrated motors may be of such manufacture, especially in the largersizes. The rotor support member, spider 12, is illustrated as aresilient member comprising a plurality of metal bars '16 extendingoutward from a hub member (17 which is bolted to a mounting support \18welded to mill shell 2. The outer ends of bars 16 are welded to a ringshaped member 19 which is connected to the rotor rim, or they may beattached directly to the rim. An end view of the rotor supporting memberis shown in FIGURE 3. An alternative form of resilient spider 12comprises recessed or cut out portions 20 in an originally solid diskrotor spider web as indicated in FIGURE 3. Resilient members 16 may alsoextend radially outward in the manner described for the FIGURE 1embodiment. Also, rotor mill.

support member 12 may be solid or split disk, with or without openings,of suflicient thinness to provide the desired resiliency or ofsufficient thickness to provide rigid support. Finally, rotor supportmember 12 may be a solid or split disk, with or without openings, butwith member 18 being of resilient construction.

FIGURE 4 illustrates a third embodiment of our invention wherein motor 8is aligned with ball mill 1 and axially spaced therefrom. An internallyflanged mill is indicated in FIGURE 4, although {it should be understoodthat such mill may be externally flanged as shown in FIGURES l, 2, and5. This third embodiment illustrates a direct driven ball mill whereinthe over-all height is reduced by extending the over-all length. Therotor of driving motor 8 is connected to hollow mill trunnion shaft 6 oran extension thereof, and is supported entirely by mill trunnion bearing7.

A fifth embodiment of our invention is illustrated in FIGURE 5, and issimilar to the embodiment illustrated in FIGURE 4. The motor rotor issupported by one (not shown) or two bearings 21 and a solid or flexibletype of shaft coupling 22 may be inserted between the motor and Therotors in the FIGURES 4 and 5 embodiments may be directly connected toshaft 6 since the thermal variation problem is minimized in suchconfigurations. In FIGURE 5, an alternative and substantially lesscostly arrangement results by inserting the mill feed or dischargebetween appropriate flanges (not shown) on the now solid motor shaft andhollow mill shaft 6 adjacent coupling 22.

Several embodiments of a gearless or direct driven rotary mill apparatushave been described and illustrated hereinabove. Over-all millmaintenance costs are reduced since gear wear and gear lubrication areeliminated. Further, the elimination of the gears reduces over-all (milland drive) length. The electric current demand for starting,accelerating, and pulling of the mill into synchronism is also reduceddue to the elimination of the inertia of the gears, and moreimportantly, due to the particular over-all characteristics which thesystem of the combined drive motor and its power supply provide. Millfeed and discharge are simplified since the path for the materialcomprises hollow mill trunnion shaft 6 and includes passage through themotor rotor in all but one of the described embodiments. Thus, themaximum size of ball mills can be increased almost indefinitely beyondthe limits presently imposed by gear driven mills.

Synchronous drive motor 8 must of necessity be a low speed, high torquemotor in order to obtain a direct drive between the motor and ball mill.However, a low speed (1020 r.p.m.), high torque synchronous motor whichis designed to be energized by conventionally available 60 cycle powermay comprise a structure having hundreds of poles, small air gap, andlow efficiency. Thus, of necessity, motor 8 must be energized from a lowfrequency (0-l5 cycles per second) power source. Conventional adjustablefrequency motor-generator sets cannot economically provide such lowfrequency power. We avoid such disadvantages by utilizing a system ofelectric valves, such as mercury arc tubes or silicon controlledrectifiers, suitably arranged and controlled to form a high power, highvoltage, frequency converter power supply. While the desired result canbe obtained by connecting a 3-phase power rectifier and inverter inseries between a source of 3-phase -60 cycle electric power and thearmature windings of the motor 8, with the inverter being designed in aknown manner to have an adjustable frequency output of the proper range(such as 0-15 cycles per second), we prefer to use the arrangement shownschematically in FIG- URE 6.

FIGURE 6 is a one-line electrical diagram of the preferred frequencyconverter power supply and the motor circuit energized thereby.Frequency and power control is accomplished by phase retardation of3-electrode electric valves (silicon controlled rectifiers) located inindividual power units of a static frequency divider circuit 23.

The circuit 23 comprises three separate pairs of reverselypoled parallelpower units, represented symbolically at 24 and '25, respectively. Eachindividual unit actually comprises a plurality of silicon controlledrectifiers interconnected to form a three-phase bridge circuit, with theDC. terminals of the paired circuits 24 and 25 being paralleled tosupply bidirectional current to the connected phase of the armaturewindings of the motor. The number of serially connected rectifierswithin each unit is determined by the voltage rating of motor 8. Thenumber of units employed in parallel is determined by the current ratingof the motor and the duty cycle of the load. The circuit 26 alsocontains protective fuses 26, surge suppression resistors andcapacitors, indicating lamps and current limiting reactors (not shown).

The respective periods of conduction of the silicon controlledrectifiers which comprise the reversely-poled power units 24 and 25 aresuitably varied and controlled, by means of the control circuit 35 shownin block form in FIGURE 6, so that these units supply the motor windingswith electric current having the desired frequency and having a waveform approximating that of a sine wave. Each pair of units is providedwith its own control circuit 35, although only one block has been shown.Techniques for designing the control circuits are known in the art.

The circuit 35 is provided with a 3-phase 60 cycle signal derived fromthe power bus 27 by way of transforming means 28, and a 3-phase variablefrequency control signal is also applied. The latter signal is derivedfrom a suitable source 29 representing for example, a small, variablefrequency three-phase alternator, although other variable frequencyalternating voltage sources may alternatively be employed. The variablefrequency signal controls the voltage and frequency of the threeseparate reversing electrical energy supplies, one for each phase of themot-or windings, to obtain balanced three phase variable frequency motorterminal voltage. The motor armature power supply is thus adapted toprovide three phase adjustable voltage which has been converted from 60cycles to a frequency range of 0 to 25 cycles per second. Since theparticular details of the control circuit 65 are not being claimed asour invention, they need not be further disclosed herein. Powertransformers 30 for reducing the voltage of the main bus 27 to thevoltage rating of the motor, main bus switchgear 3'1, rectifierisolating circuit breakers 32, and suitable means 3 3 for detecting andlimiting ground faults in the motor comprise the remainder of the majorcomponents in the adjustable frequency synchronous motor armature powersupply. A typical main power bus 27, which distributes three phase, 60cycle power at 4160 volts is shown by way of example.

A motor field energizing circuit, including rectifying means 34,provides field excitation for the motor rotor. The field circuit isshown connected to the main power bus through transforming and switchingmeans.

The power supply described hereinabove permits the use of a synchronousmotor 8 having such desirable characteristics as, a practical number offield poles having reasonably sized pole pitches (and thus a motor ofmoderate physical size), high efficiency (approximately and a relativelylarge rotor-stator air gap (approximate-1y 0.4 inch) which readilypermits mounting of the rotor on support members as describedhereinabove.

From the foregoing description, it can be appreciated that our inventionmakes available a direct-driven or gearless rotary mill which isespecially adapted for high torque, low speed applications. Gearlesstype drives have not previously been utilized for such applications, andthis is especially true in ball mills. The means employed forresiliently or rigidly mechanically coupling the motor rotor to the milland the use of a static frequency conversion power supply permits thepractical use of low speed, low frequency motors and thereby achievesour invention.

Having described a new gearless rotary mill, it is believed obvious thatmodifications and variations of our invention are possible in the lightof the above teachings. Thus, the motor rotor may be supported from themill in spaced apart relationship by members having a variety ofconfigurations other than disclosed hereinabove. In particular, therotor may be directly connected to an extension of mill flange 3 or headflange '5. Further, the power supply for the motor armature may utilizeother rectifying means such as ignitron (mercury arc) tubes. Finally thedriving motor need not be limited to the synchronous type and may be analternating current wound rotor induction motor or a direct currentmotor. These latter type motors are not preferred, however, for thefollowing reasons. In the direct current motor, the size and cost islarge and presents the problem of splitting the commutator. In theinduction type motor, the in- .herently small air gap creates problemsin mounting the rotor around the mill shell, it is also difficult tosplit the rotor, and still maintain good efficiency and power factor. Itis therefore, to be understood that changes may be made in theparticular embodiments of our invention described which are within thefull intended scope of the invention as defined by the following claims.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

1. A relatively low speed gearless rotary mill adapted to minimizemechanical stresses which are induced within the rotor of a drivingmotor due to unequal thermal expansions and contractions within therotor and mill members, comprising a rotary mill comprising a rotatablereceptacle for treating material in said receptacle while saidreceptacle is being rotated, and

an electric motor having a rotor and stator, said stator beingstationarily mounted, said rotor being spaced from said receptacle andresiliently supported therefrom whereby said receptacle is rotated bysaid motor through a resilient gearless driving arrangement whichminimizes mechanical stresses that tend to be developed Within the motorrotor due to unequal temperature conditions resulting from mill andmotor operation.

2. A direct-driven ball mill comprising a ball mill comprising arotatable receptacle for treating material in said receptacle while saidreceptacle is being rotated, means for feeding the material to anddischarging the material from said receptacle, said receptacle having aball mill flange at each end thereof,

a mill head at each end of said ball mill and aligned therewith, eachsaid mill head comprising a large diameter end and a small diameter end,said large diameter end having a mill head flange connected to said ballmill flange,

an electric motor having a rotor and stator disposed in encirclingconcentric relationship to said ball mill, said stator beingstationarily mounted, said rotor being spaced from said receptacle, and

means for resiliently connecting the rotor of said motor to one of saidball mill flanges whereby said ball mill is rotated by said motorthrough a resilient gearless driving arrangement.

3. A direct-driven ball mill comprising a ball mill comprising arotatable receptacle for treating material in said receptacle while saidreceptacle is being rotated, means for feeding the material to anddischarging the material from said receptacle, said receptacle having aball mill flange at each end thereof,

a mill head at each end of said ball mill and aligned therewith, eachsaid mill head comprising a large diameter end and a small diameter end,said large diameter end having a mill head flange connected to said ballmill flange,

an electric motor having a rotor and stator disposed in encirclingconcentric relationship to said ball mill, said stator beingstationarily mounted, said rotor being spaced from said receptacle, and

a rotor spider member for supporting said rotor from said receptacle inspaced apart relation, said spider member comprising an inner diskmember attached to said receptacle, an intermediate offset web member,and an outer member attached to the motor rotor.

4. The apparatus set forth in claim 3 wherein said outer membercomprises -a plurality of outwardly extending steel bars having crosssections sufficiently small whereby said rotor is resiliently supportedon said receptacle.

5. The apparatus set forth in claim 3 wherein said outer membercomprises a solid disk having a cross section sufliciently thick wherebysaid rotor is rigidly supported on said receptacle.

6. A direct-driven ball mill comprising a ball mill comprising arotatable receptacle for treating material in said receptacle while saidreceptacle is being rotated, means for feeding the material to anddischarging the material from said receptacle, said receptacle having aball mill flange at each end thereof,

a mill head at each end of said ball mill and aligned therewith, eachsaid mill head comprising a large diameter end and a small diameter end,said large diameter end having a mill head flange connected to said ballmill flange,

a synchronous motor having a speed rating in the range 0 to 40revolutions per minute and a frequency rating in the range 0 to 15cycles per second, said motor having a rotor and stator, said statorbeing stationarily mounted, said rotor being spaced from said receptaclein encircling concentric relationship and mechanically coupled theretowhereby said motor is connected to said ball mill through a gearlessdriving arrangement, and

static frequency conversion means for supplying alter- I nating currentelectrical energy of frequency adjustable in the range of at least 0 to15 cycles per second to said motor stator.

References Cited by the Examiner UNITED STATES PATENTS 1,224,933 5/17Jordan 24-1-176 1,585,566 5/26 Sindl 310-157 1,674,516 6/28 Lunz 310-402,175,321 10/39 Saflir 2 4 1-176 X 2,791,734 5/57 Kielfert 318-17 12,814,769 11/57 Williams 318-171 3,028,104 4/62 Hall 241-176 3,033,0575/62 Gray 259-175 X 3,051,399 8/62 Stauffer 241-176 3,105,180 9/63Burnett 318-341 X 3,109,131 10/63 Byrd 318-341 X 3,172,546 3/65Schreiner 241-176 X ROBERT C. RIORDON, Primary Examiner. H. F. PEPPER,Assistant Examiner.

1. A RELATIVELY LOW SPEED GEARLESS ROTARY MILL ADAPTED TO MINIMIZEMECHANICAL STRESSES WHICH ARE INDUCED WITHIN THE ROTOR OF A DRIVINGMOTOR DUE TO UNEQUAL THERMAL EXPANSIONS AND CONTRACTIONS WITHIN THEROTOR AND MILL MEMBERS, COMPRISING A ROTARY MILL COMPRISING A ROTATABLERECEPTACLE FOR TREATING MATERIAL IN SAID RECEPTACLE WHILE SAIDRECEPTACLE IS BEING ROTATED, AND AN ELECTRIC MOTOR HAVING A ROTOR ANDSTATOR, SAID STATOR BEING STATIONARILY MOUNTED, SAID ROTOR BEING SPACEDFROM SAID RECEPTACLE AND RESILIENTLY SUPPORTED THEREFROM WHEREBY SAIDRECEPTACLE IS ROTATED BY SAID MOTOR THROUGH A RESILIENT GEARLESS DRIVINGARRANGEMENT WHICH MINIMIZE MECHANICAL STRESSES THAT TEND TO BE DEVELOPEDWITHIN THE MOTOR ROTOR DUE TO UNEQUAL TEMPERATURE CONDITIONS RESULTINGFROM MILL AND MOTOR OPERATION.